Windows only: Dexrex, a free set of plug-ins for most popular IM clients, lets you store transcripts of your IM conversations from any system online for later reference. Dexrex's plug-ins work with Digsby, Pidgin, AIM Messenger, Yahoo Messenger, and many more—see the video below for a demonstration. You can even import older, locally-saved chat logs onto the site for a complete archive, or sign into chat directly through Dexrex's site, while automatically saving transcripts. Whether or not you trust your chat logs to an online storage site is up to you, of course, but it's definitely helpful if you trade a lot of links and important info through chat. Dexrex's extensions are free downloads for Windows chat clients only. Here's a video showing off some of Dexrex's features: